District energy distribution system and method of providing mechanical work and heating heat transfer fluid of a district thermal energy circuit

ABSTRACT

A district energy distributing system comprising a geothermal power plant comprising a first and a second circuit. The first circuit comprises a feed conduit for an incoming flow of geothermally heated water from a geothermal heat source; a boiler comprising a heat exchanger configured to exchange heat from the incoming flow of geothermally heated water to superheat a working medium of a second circuit of the geothermal power plant; and a return conduit for a return flow of cooled water from the boiler to the geothermal heat source. The second circuit comprises the boiler configured to superheat the working medium of the second circuit; an expander configured to allow the superheated working medium to expand and to transform the expansion to mechanical work; and a condenser configured to transform the expanded working medium to liquid phase and to heat a heat transfer fluid of a district thermal energy circuit.

FIELD OF THE INVENTION

The invention relates to a district energy distributing system and amethod of providing mechanical work and heating heat transfer fluid of adistrict thermal energy circuit.

BACKGROUND OF THE INVENTION

Nearly all large developed cities in the world have at least two typesof energy grids incorporated in their infrastructures; one grid forproviding electrical energy and one grid for providing space heating andhot tap water preparation. A common grid used for providing spaceheating and hot tap water preparation is a gas grid providing a burnablegas, typically a fossil fuel gas. The gas provided by the gas grid islocally burned for providing space heating and hot tap water. Analternative for the gas grid for providing space heating and hot tapwater preparation is a district heating grid. Also the electrical energyof the electrical energy grid may be used for space heating and hot tapwater preparation. Also the electrical energy of the electrical energygrid may be used for space cooling. The electrical energy of theelectrical energy grid is further used for driving refrigerators andfreezers.

Accordingly, traditional building heating and cooling systems useprimary high grade energy sources such as electricity and fossil fuelsor an energy source in the form of industrial waste heat to providespace heating and/or cooling, and to heat or cool water used in thebuilding. Furthermore, it has been increasingly common to also install adistrict cooling grid in cities for space cooling. The process ofheating or cooling the building spaces and water converts this highgrade energy into low grade waste heat with high entropy which leavesthe building and is returned to the environment.

It is also well known to use geothermal heat source systems using theheat energy available in the earth to generate e.g. electricity ormechanical work. These kind of systems do however release a large ofamount of heat energy which is released by to the ambience by e.g.cooling towers.

Hence, there is a need for an improved and cost-effective system tobetter use available waste heat.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve at least some of theproblems mentioned above.

According to a first aspect, a district energy distributing system isprovided. The district energy distributing system comprises a geothermalpower plant comprising: a first circuit comprising: a feed conduit foran incoming flow of geothermally heated water from a geothermal heatsource;

a boiler comprising a heat exchanger configured to exchange heat fromthe incoming flow of geothermally heated water to superheat a workingmedium of a second circuit of the geothermal power plant; a returnconduit for a return flow of cooled water from the boiler to thegeothermal heat source; wherein the second circuit comprises: the boilerconfigured to superheat the working medium of the second circuit; anexpander connected to the boiler and configured to allow the superheatedworking medium to expand and to transform the expansion to mechanicalwork; and a condenser configured to transform the expanded workingmedium to liquid phase and to heat a heat transfer fluid of a districtthermal energy circuit; wherein the district thermal energy circuitcomprises: a district feed conduit; a district return conduit; aplurality of local heating systems, each having an inlet connected tothe district feed conduit and an outlet connected to the district returnconduit, wherein each local heating system is configured to provide hotwater and/or comfort heating to a building; and the condenser configuredto heat heat transfer fluid of the district feed conduit to atemperature of 5-30° C.

The district energy distribution system is configured to combine ageothermal heat source system with a district energy distributing systemand with a geothermal power plant. Accordingly, the energy that isextracted from the geothermally heated water may supplied to a pluralityof local heating systems which may be used to provide hot water and/orcomfort heating to a building. The district energy distribution systemcan also be used to return energy to the geothermal heat source by thecentral heat exchanger. Further, the energy that is extracted from thegeothermally heated water may be used to generate mechanical work, whiche.g. can be used to generate electrical power.

Geothermal energy is in the context of the application to be understoodas heat energy that is generated and stored in the earth. Geothermalenergy is cost-effective, reliable, sustainable, and environmentallyfriendly but has historically been limited to areas near tectonic plateboundaries. Recent technological advances have however dramaticallyexpanded the range and size of viable resources, especially forapplications such as home heating, opening a potential for widespreadexploitation. Developments in drilling allows that geothermal heatsource systems can be engineered at depths of up to 5 km or even more.Systems providing access to that kind of depths are often referred to asdeep geothermal heat source systems. The inlet and outlet holes to thebedrock are typically arranged at a large distance from each other.Further, the bedrock in the area between the inlet and outlet holes isfractioned allowing water to be stored in the thus formed interspaces.The bedrock as such may be dry, whereby the water is actively suppliedvia the inlet hole to the bedrock where it is heated. Such formedunderground storage is in the following referred to as a geothermal heatsource.

By the provided district energy distribution system, a number ofadvantages are made possible.

The fluctuating temperature in the district energy distribution systemin terms of higher temperatures in the summer with low heat load andlower temperatures in the winter with high heat load, results in thatthe power plant forming part of the system will be able to generate moreelectricity during the winter, (increased power vs heat ratio), i.e.during the period of high heat load. This provides an advantage overdistrict energy systems were a situation of high load always is followedby a higher delivery temperature of the heat fluid and with a subsequentpressure increase in the condenser which as such results in a lowerpower vs heat ratio during the winter.

The potential heat power increases substantially (more or less twice)since the condenser operates in the temperature interval of 0-30° C.instead of the typical temperature interval of 45-120° C. which appliesto traditional district energy distribution systems. In fact, moreelectrical power may be generated as compared to a situation where allsurplus heat instead would have to be removed as waste heat by usinge.g. cooling towers.

The provided district energy distribution system which is configured tocontrol the temperature of the outgoing flow of heat transfer fluid inthe district feed conduit to a temperature of 5-30° C. may be seen as alow-temperature system as a difference to typical district energydistribution systems that typically operate in the interval 45-120° C.Thereby a number of advantages are made possible. By way of example, aconsiderably higher efficiency and amount of heat (up to 3 times) can begained from an identical geothermal system when the temperaturedifference increases as a result of the low temperature demandsregarding distribution and consumption as compared to traditionaldistrict energy distribution systems.

Also, normal geothermal technology provides a working life of about20-30 years before the heat in the used bedrock has been consumed. Theheat is typically considered as being consumed when the deliverytemperature in the bedrock has reached the minimum delivery temperaturewhich is deemed acceptable to a district heating system. For the record,the acceptable minimum delivery temperature is typically 80-120° C. fora normal district heating system. By the present district energydistribution system, in combination with inherent fluctuations intemperature between winter and summer, i.e. periods of high heat loadand low heat load, the geothermic energy system can be used as a largegeothermal storage. More precisely, heat can be transferred to thegeothermal heat source during the summer, which is a period of low heatload. Likewise, heat can be extracted during the winter which is aperiod of high heat load. Thereby the bedrock forming part of thegeothermic source can be continued to be used also when the deliverytemperature of the heated water is lower than 15-30° C., but then as aseason storage. Thus, by the provided district energy distributionsystem, the otherwise inherent limited working life of a geothermalsource does no longer apply.

The geothermal heat source may be a deep geothermal heat source.

The expander may be a gas turbine. As a non-limiting example, the gasturbine may be a steam turbine.

The expander may be configured to allow the superheated working mediumto expand to receive an outgoing temperature of 10-40° C.

The boiler may be configured to superheat the liquefied working mediumfrom the condenser.

The geothermal power plant may further comprise a generator configuredto transform the mechanical work into electrical power.

The geothermal heat source may be configured to geothermally heat thecooled water returned via the return conduit to a temperature of100-250° C.

The first circuit may further comprise a suction pump configured to drawgeothermally heated water from the geothermal heat source to the feedconduit, and pressurize the geothermally heated water such that it is inliquid phase in the feed conduit.

The boiler may be configured to exchange heat from the incoming flow ofgeothermally heated water such that the cooled water in the returnconduit has a temperature of 10-40° C.

The district feed conduit may together with the district return conduithave a heat transfer coefficient greater than 2.5 W/(mK) when parallelarranged in ground. This value of the heat transfer coefficient isestimated when the local feed and return conduits are parallel arrangedwithin a distance of one meter from each other in ground having anaverage annual temperature of 8° C. and the arithmetic averagetemperature of the local feed and return conduits are 8-10° C. By this,thermal heat from the surroundings may be picked up by the local feedconduit and/or the local return conduit. Moreover, cheap un-insulatedplastic pipes may be used for the local feed conduit and/or the localreturn conduit. Moreover, thermal energy of the surroundings may easilybe absorbed by the local heat transfer fluid flowing in the local returnconduit.

The district feed conduit may be configured to allow heat transfer fluidof a first temperature to flow there through, and wherein the districtreturn conduit may be configured to allow heat transfer fluid of asecond temperature to flow there through, wherein the second temperatureis lower than the first temperature, and wherein each of the localheating systems may comprise: a thermal energy consumer heat exchangerselectively connected to the district feed conduit via a thermal energyconsumer valve for allowing heat transfer fluid from the district feedconduit to flow into the thermal energy consumer heat exchanger,selectively connected to the district feed conduit via a thermal energyconsumer pump for pumping heat transfer fluid from the hot conduit intothe thermal energy consumer heat exchanger, and connected to thedistrict return conduit for allowing return of heat transfer fluid fromthe thermal energy consumer heat exchanger to the district returnconduit, wherein the thermal energy consumer heat exchanger may bearranged to transfer thermal energy from heat transfer fluid tosurroundings of the thermal energy consumer heat exchanger, such thatheat transfer fluid returned to the cold conduit has a temperature lowerthan the first temperature and preferably a temperature equal to thesecond temperature; a pressure difference determining device configuredto determine a local pressure difference, Δp1, between the district feedconduit and the district return conduit; and a controller configured to,based on the local pressure difference, selectively control the use ofeither the thermal energy consumer valve or the thermal energy consumerpump.

The wording “selectively connected” should be construed as the heatexchanger concerned is at one point in time in fluid connection eithervia the pump or via the valve to the respective conduit. Hence, it maybe selected if the heat exchanger concerned shall be in fluid connectionwith the respective conduit via the pump or via the valve.

The wording “valve” should be construed as a device configured to, in acontrolled way, allowing heat transfer fluid to flow through the valvewhen the valve is in an opened state. Moreover, the valve may also bearranged such that the flow rate of heat transfer fluid through thevalve may be controlled. Hence, the valve may be a regulation valvearranged for regulating the flow of heat transfer fluid there trough.

The wording “pump” should be construed as a device configured to, in acontrolled way, allowing heat transfer fluid to be pumped through thepump when the pump is in an active pumping state. Moreover, the pump mayalso be arranged such that the flow rate of heat transfer fluid throughthe pump may be controlled.

The pump and the valve may together be seen as a flow regulatorselectively acting as a pump or as a valve. The wording “selectively actas a pump or a valve” should be construed as the flow controller is atone point in time acting as a pump and at another point in time actingas a valve. Such a flow regulator is described in the patent applicationEP16205021.5.

The district thermal energy distribution system allows for the localpressure difference between heat transfer fluid of the district feedconduits and the district return conduits, i.e. the hot and coldconduits to vary along the thermal energy circuit. Especially, the localpressure difference between heat transfer fluid of the district feedconduits and district return conduits may vary from positive to negativepressure difference seen from one of the conduits. The district thermalenergy distribution system further allows for the possibility to let allthe pumping within the system to take place in the local thermal energyconsumer/generator assemblies. Due to the limited flows and pressuresneeded small frequency controlled circulation pumps may be used. Hence,an easy to build district thermal energy distribution system isprovided. Further a district thermal energy distribution system that iseasy to control is provided.

The basic idea of the district thermal energy distribution system isbased on the insight by the inventors that modern day cities by themself-provided thermal energy that may be reused within the city. Thereused thermal energy may be picked up by the district thermal energydistribution system and be used for e.g. space heating or hot tap waterpreparation. Moreover, increasing demand for space cooling will also behandled within the district thermal energy distribution system. Withinthe district thermal energy distribution system buildings within thecity are interconnected and may in an easy and simple way redistributelow temperature waste energy for different local demands. Amongst otherthe district thermal energy distribution system will provide for:

-   -   Minimizing the use of primary energy due to optimal re-use of        energy flows inside the city.    -   Limiting the need for chimneys or firing places inside the city,        since the need for locally burning gas or other fuels will be        reduced.    -   Limiting the need for cooling towers or cooling convectors        inside the city, since excess heat produced by cooling devices        may be transported away and reused within the district thermal        energy distribution system.

Hence, the district thermal energy distribution system using geothermalenergy provides for a smart duel use of thermal energy within a city.When integrated into a city the district thermal energy distributionsystem provides make use of low level thermal energy waste in bothheating and cooling applications within the city. This will reduce theprimary energy consumption of a city by eliminating the need for a gasgrid or a district heating grid and a cooling grid in city.

The controller may be configured to selectively use the thermal energyconsumer valve when the local pressure difference indicates that a localpressure of the heat transfer fluid of the district feed conduit islarger than a local pressure of the heat transfer fluid of the districtreturn conduit, wherein the controller may be configured to selectivelyuse the thermal energy consumer pump when the first local pressuredifference indicates that the first local pressure of the heat transferfluid of the district feed conduit is lower than or equal to the firstlocal pressure of the heat transfer fluid of the district returnconduit.

Each of the plurality of local heating systems may be configured toextract heat from heat transfer fluid entering the local heating systemvia the inlet and return the thereafter cooled heat transfer fluid tothe district return conduit via the outlet, wherein each of theplurality of local heating systems may be configured to return localheat transfer fluid having a temperature in the range of −5-15° C. Byconducting local heat transfer fluid having a temperature in thistemperature range, heat loss to the surroundings may be reduced.Moreover, thermal energy of the surroundings may even be absorbed by thelocal heat transfer fluid flowing in the local return conduit. Thesurroundings of the district return conduit is typically ground sincethe district return and feed conduits typically are arranged in theground along the majority of their paths.

The district feed conduit and district return conduit may be dimensionedfor pressures up to 0.6 MPa, 1 MPa, or 1.6 MPa.

The boiler may comprise a plurality of heat exchangers connected inseries in the first and second circuits. As seen in the flow directionof the first circuit, the boiler may comprise a superheater, a boilerand an economizer. The flows in the first and second circuits pass theboiler as two counter flows.

The feed conduit may be configured to allow heat transfer fluid of afirst temperature to flow there through, and the return conduit may beconfigured to allow heat transfer fluid of a second temperature to flowthere through, wherein the second temperature may be lower than thefirst temperature.

The first and second local pressure differences may be set to be at most±0.2 MPa, ±0.3 MPa or ±0.6 MPa depending on chosen dimensioningpressure.

The temperature difference between the temperatures of the district feedconduit and the district return conduit may be in the range of 5-16° C.,preferably in the range of 7-12° C., more preferably 8-10° C.

According to another aspect, a method of providing mechanical work andof heating heat transfer fluid of a district thermal energy circuit isprovided. The method comprises: supplying to a boiler which is connectedto a geothermal heat source, a flow of geothermally heated water fromthe geothermal heat source; exchanging, by a heat exchanger of theboiler, heat from the incoming flow of geothermally heated water tosuperheat a working medium; expanding, in an expander, the superheatedworking medium providing mechanical work; and transforming, at acondenser, the expanded working medium to liquid phase by heating a heattransfer fluid of a district feed conduit in the district thermal energycircuit to a temperature of 5-30° C.

A further scope of applicability of the present invention will becomeapparent from the detailed description given below. However, it shouldbe understood that the detailed description and specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only, since various changes and modifications within thescope of the invention will become apparent to those skilled in the artfrom this detailed description.

Hence, it is to be understood that this invention is not limited to theparticular component parts of the device described or steps of themethods described as such device and method may vary. It is also to beunderstood that the terminology used herein is for purpose of describingparticular embodiments only, and is not intended to be limiting. It mustbe noted that, as used in the specification and the appended claim, thearticles “a,” “an,” “the,” and “said” are intended to mean that thereare one or more of the elements unless the context clearly dictatesotherwise. Thus, for example, reference to “a unit” or “the unit” mayinclude several devices, and the like. Furthermore, the words“comprising”, “including”, “containing” and similar wordings does notexclude other elements or steps.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be describedin more detail, with reference to the appended drawings showingembodiments of the invention. The figures are provided to illustrate thegeneral structures of embodiments of the present invention. Likereference numerals refer to like elements throughout.

FIG. 1 is a schematic diagram of an energy distribution system.

FIG. 2 is a schematic diagram of a local heating system.

FIG. 3 is a schematic diagram of a combined heating and cooling system.

FIG. 4 is a schematic diagram of a local thermal energy consumerassembly and a local thermal energy generator assembly connected to athermal energy circuit.

FIG. 5 is a block diagram of a method of providing mechanical work andheating heat transfer fluid of a district thermal energy circuit.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which currently preferredembodiments of the invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided for thoroughness and completeness, and to fully convey thescope of the invention to the skilled person.

In connection with FIG. 1 an energy distribution system will bediscussed. The energy distribution system comprises a geothermal energyplant 50 having a first and a second circuit which are interconnectedvia a boiler 51. The flows of the first and second circuits are arrangedas two counter flows past the boiler 51. The first circuit is connectedto a geothermal heat source system 5 and the second circuit is connectedto a district thermal energy circuit 20.

Starting with the geothermal heat source system 5, this comprises ageothermal heat source 10. The geothermal heat source 10 communicateswith the first circuit of the geothermal energy plant 50 via a feedconduit 11 and a return conduit 12. To facilitate the circulating flow,the feed conduit 11 comprises a suction pump 13 which sucks heated waterfrom the bedrock into the first circuit. The suction pump 13 isconfigured to draw geothermally heated water from the geothermal heatsource 10 to the feed conduit 11 and pressurize the geothermally heatedwater such that it is in liquid phase in the feed conduit 11.

The return conduit 12 comprises a pump 14 which forces the cold waterfrom the first circuit back into the geothermal heat source 10. Thegeothermal heat source 10 may be configured to geothermally heat thecooled water which is returned via the return conduit 12 to atemperature of 100-250° C.

The geothermal heat source system 5 may be a deep geothermal heat sourcesystem. A deep geothermal heat source system is to be understood as asystem providing access to depths more than 3 km, preferably more than 5km.

As given above, the geothermal energy plant 50 comprises a first and asecond circuit which are interconnected by a boiler 51. Starting withthe first circuit, this comprises the feed conduit 11 for the incomingflow of geothermally heated water from the geothermal heat source 10 tothe boiler 51. The boiler 51 forms a heat exchanger which is, in FIG. 1shown embodiment, divided into three units connected in series—asuperheater 52 a, a boiler 52 b and an economizer 52 c. The boiler 51 isconfigured to exchange heat from the incoming flow of geothermallyheated water in the first circuit such that the cooled water which isreturned from the boiler 51 to the geothermal heat source 10 via thereturn conduit 12 has a temperature of 10-40° C. In the in FIG. 1 shownembodiment the boiler comprises three different heat exchanger units 52a, 52 b, 52 c, however, it is realized that any number of heat exchangerunits may be used fitting the particular set-up of the boiler 52.

Now turning to the second circuit of the geothermal energy plant 50, thesecond circuit comprises the boiler 51, an expander 53 connected to theboiler 51, and a condenser 55.

The boiler 51 with its exchanger units 52 a, 52 b, 52 c is configured toexchange heat from the incoming flow of geothermally heated water in thefirst circuit to thereby superheat a working medium of the secondcircuit of the geothermal power plant 50. The working medium of thesecond circuit may by way of example be water, ammonia, oils or propane.

The expander 53 which is connected to the boiler 51 is configured toallow the superheated working medium to expand and to transform theexpansion into mechanical work. The expander 53 may be a turbine, suchas a gas turbine. Alternatively, the expander 53 may be a Sterlingmotor. The expander 53 may be configured to allow the superheatedworking medium to expand to receive an outgoing temperature of 10-40° C.

The expander 53 may be connected to a generator 54, whereby themechanical work provided by the expander 53 may be transformed toelectrical power. The electrical power may be supplied to the electricalgrid (not shown), which as such is well known in the art.

The condenser 55 is configured to transform the expanded working mediumof the second circuit to liquid phase. The condenser 55 is alsoconfigured to heat a heat transfer fluid of the district thermal energycircuit 20.

As indicted above, the flows of the first and second circuits arearranged as two counter flows past the boiler 51. In the first circuit,the flow of hot water from the feed conduit 11 passes the boiler 51 bypassing the heat exchanger unit(s), e.g. the superheater 52 a, theboiler 52 b and the economizer 52 c, of the boiler 51 before beingreturned as cooled water to the geothermal heat source system 5 via thereturn conduit 12. Likewise, in the second circuit, the flow of cooled,liquidized working medium delivered from the condenser 55 is arranged topass the boiler 51 towards the expander 53 via the heat exchangerunit(s), e.g. the economizer 52 c, the boiler 52 b and then thesuperheater 52 a, of the boiler 51. Accordingly, the boiler 51 can beseen as a heat exchanger.

The second circuit of the geothermal energy plant 50 is connected to thedistrict thermal energy circuit 20 via the condenser 55.

The district thermal energy circuit 20 comprises a district feed conduit22 and a district return conduit 23. The district feed conduit 22 isconnected to an outlet of the condenser 55 and the district returnconduit 23 is connected to an outlet of the condenser 55. The districtthermal energy circuit 20 is configured to deliver heat transfer fluidto local heating systems 200, 250 and/or local cooling systems 300, 350which are arranged in buildings 40. The buildings may be residentialhomes but it may also be other types of buildings 40 such as officebuildings, business premises and factories in need for heating and/orcooling. It is to be understood that the district thermal energy circuitmay comprise a plurality of local heating systems 200, 250 and/or localcooling systems 300, 350.

The condenser 55 configured to exchange heat from an, via the districtfeed circuit 22, incoming flow of heat transfer fluid to an outgoingflow of heat transfer fluid in the district feed conduit 22. Thecondenser 55 is configured to exchange heat such that the outgoing flowof heat transfer fluid has a temperature of 5-30° C. Further, thecondenser 55 may be configured to exchange heat such that the districtheat transfer fluid returned to the district return conduit 23 is havinga temperature of 5-10° C. By returning heat transfer fluid of this lowtemperature, the cooling performed in the condenser 55 can be as greatas approximately 100° C. (depending of the temperature of the incomingheat transfer fluid feed through the district feed conduit 22). Thishigh degree of cooling performed in the condenser 55 will reduce theheat losses in the district heating grid. Moreover, it will reduce thedegree of pumping needed in the district heating grid.

The piping used for the district feed and return conduits 22, 23 in thedistrict thermal energy circuit 20 is normally plastic un-insulatedpiping. In this context un-insulated shall be construed such that thepiping does not have an extra layer of heat insulating material wrappedaround the same. The piping is typically designed for a maximum pressureof 0.6-1 MPa. The piping is further typically designed for maximumtemperature of about 50° C. Further, the district feed and returnconduits 22, 23 in the district thermal energy circuit 20 may togetherhave a heat transfer coefficient greater than 2.5 W/(mK) when parallelarranged in ground. As mentioned above, this value of the heat transfercoefficient is estimated when the district feed and return conduits 22,23 are parallel arranged within a distance of one meter from each otherin ground having an average annual temperature of 8° C. and thearithmetic average temperature of the local feed and return conduits are8-10° C.

The heat transfer fluid, and hence energy carrier, is typically water,although it is to be understood that other fluids or mixture of fluidsmay be used. Some non-limiting examples are ammonia, anti-freezingliquids (such as glycol), oils and alcohols. A non-limiting example of amixture is water with an anti-freezing agent, such as glycol, addedthereto. According to a preferred embodiment the heat transfer fluid isa mixture of water and an anti-freezing agent, such as glycol. This willallow for the heat transfer fluid to have temperatures below 0° C.Providing a heat transfer fluid having freezing point below 0° C.,preferably below −5° C., makes it possible to conduct heat transferfluid in the district return conduit 23 that may absorb heat from thesurroundings, e.g. the ground surrounding the district return conduit23, even if the surroundings have a temperature close to 0° C.

Now with reference to FIG. 2, a local heating system 200 will bediscussed in more detail. The district thermal energy circuit 20 maycomprise one or more local heating systems 200 of this type.

The local heating system 200 comprises a heat pump 201 and a heatemitter 202. The heat emitter 202 is connected to the local energydistributing grid 20 a via the heat pump 202. The local heating system200 is configured to, via the heat emitter 202 and the local heat pump201, provide hot tap water and/or comfort heating to a respectivebuilding 40. The local heat pump 201 has an inlet 25 connected to thedistrict feed conduit 22 and an outlet 26 connected to the districtreturn conduit 23. In this context the term “inlet of the heat pump” isto be interpreted as the inlet via which the heat pump is fed with localheat transfer fluid from the district thermal energy circuit 20.Likewise, the term “outlet of the heat pump” is to be interpreted as theoutlet via which the heat pump returns local heat transfer fluid to thedistrict thermal energy circuit 20.

Heat pumps as such, are well known in the art and basically comprises aclosed circuit in which brine is circulated between a first heatexchanger and a second heat exchanger. The first heat exchanger has aninlet and an outlet, in this case the inlet 25 and the outlet 26 of thelocal heat pump 201, via which the local heat pump 201 is connected to afirst circuit circulating a flow of a first fluid, in this case the heattransfer fluid of the district thermal energy circuit 20. Likewise, thesecond heat exchanger has an inlet and an outlet via which the localheat pump 201 is connected to a second circuit circulating a flow of asecond fluid, in this case a heating fluid of the heat emitter 202. Theheating fluid of the heat emitter 202 is typically water, although it isto be understood that other fluids or mixture of fluids may be used.Some non-limiting examples are ammonia, anti-freezing liquids (such asglycol), oils and alcohols. A non-limiting example of a mixture is waterwith an anti-freezing agent, such as glycol, added thereto.

Since the flow of heat transfer fluid in the district feed conduit 22 ishaving a temperature of 5-30° C. the input temperature to the local heatpump 201 is in the same temperature range. The local heating system 200is configured to extract heat from heat transfer fluid entering thelocal heat pump 201 via the inlet 25 and return heat transfer fluid tothe district return conduit 23 via the outlet 26. The local heatingsystem 200 is configured to return local heat transfer fluid having atemperature being in the range of −5-15° C.

The local heating system 200 may further comprises a local circulationpump 203. In the in FIG. 2 shown embodiment the local circulation pump203 is arranged in the outlet 26 of the local heat pump 24. However, thelocal circulation pump 28 may alternatively be arranged in the inlet 25of the local heat pump 201. Hence, the local circulation pump 203 isconnected between the inlet 25 and the outlet 26 of the local heatingsystem 200. The local circulation pump 203 is configured to circulateheat transfer fluid in the district feed conduit 22 and the districtreturn conduit 23. The local circulation pump 203 is configured toovercome the pressure difference between the district return conduit 23and the district feed conduit 22. The local circulation pump 203 isfurther configured to regulate the flow of heat transfer fluid flowingthrough the local heat pump 201. By regulating the flow of cooling fluidtrough the local heat pump 201, and at the same time optionally controlthe operation of the local heat pump 201, the temperature of the localheat transfer fluid outputted from the local heat pump 201 may becontrolled.

Hence, some or all of the plurality of local heating systems 200 of thedistrict thermal energy system 20 may comprise a local circulation pump203 for circulating heat transfer fluid in the district feed conduit 22and in the district return conduit 23. Additionally, or in combinationwith the plurality of local circulation pumps 203, the district thermalenergy circuit 20 may comprise a central circulation pump 27 configuredto circulate the fluid in the district feed and return conduits 22, 23.The central circulation pump 27 is best seen in FIG. 1.

The local heat pump 201 may be controlled by a controller 204. Thecontroller 204 may control the local heat pump 201 based on datapertaining to heating demands of the heat emitter 202 and/or datapertaining to the temperature of the heat transfer fluid in the outlet26 of the local heat pump 201. Data pertaining to heating demands of theheat emitter 202 may be determined by means of a heat demand sensor 205connected to the heat emitter 202. Data pertaining to the temperature ofthe local heat transfer fluid in the outlet 26 of the heat pump 201 maybe determined by means of a temperature sensor T1 connected to theoutlet 26.

Now with reference to FIG. 3, a local cooling system 300 will bediscussed in more detail. The district thermal energy circuit 20 maycomprise one or more local heating systems 300.

It shall be noted that the local cooling system 300 is arranged inconnection with a local heating system 200. The local heating system 200is a local heating system of the type that has been discussed above withreference to FIG. 2. In order to avoid undue repetition with regard tothe local heating system 200 reference is made to the above.

Each local cooling system 300 comprises a cooler 301 and a cooling heatexchanger 302. Coolers 301 are as such well known in the art and may beused e.g. for comfort cooling in buildings such as office buildings,business premises, residential homes and factories in need for cooling.The cooler 301 is connected to the district thermal energy circuit 20via the cooling heat exchanger 302. The local cooling system 300 isconfigured to, via the cooler 301 and the cooling heat exchanger 302,provide comfort cooling to a respective building 40. Hence, the localcooling system 300 is configured to extract heat from a building 40.

The cooling heat exchanger 302 has an inlet 303 connected to the outlet26 of one of the plurality of local heating systems 200. The coolingheat exchanger 302 further has an outlet 304 connected to the districtreturn conduit 23 of the district thermal energy circuit 20. In thiscontext the term “inlet of the heat exchanger” is to be interpreted asthe inlet via which the heat exchanger is fed with local heat transferfluid from the district thermal energy circuit 20. Likewise, the term“outlet of the heat exchanger” is to be interpreted as the outlet viawhich the heat exchanger returns local heat transfer fluid to thedistrict thermal energy circuit 20.

As mentioned above, the cooler 301 is connected to the district thermalenergy circuit 20 via the cooling heat exchanger 302. With reference tothe above, heat exchangers as such are well known in the art and canbasically be described as comprising an arrangement of a first closedcircuit circulating a first fluid having a first temperature, and asecond closed circuit circulating a second fluid having a secondtemperature. By the two circuits along an extension closely abuttingeach other a heat transfer takes place between the two fluids. In thelocal cooling system 300, the first circuit is locally arranged in thebuilding 40 and the second circuit forms part of the district thermalenergy circuit 20. Coolers to be used for local cooling systems ofbuildings are typically situated in air ducts of ventilation ordistributed through fan-driven air-coil collectors or ceiling mountedcooling batteries in individual spaces of a building.

The local cooling system 300 may further comprise a flow valve 305. Theflow valve 305 is configured to regulate the flow of local heat transferfluid flowing through the cooling heat exchanger 302. By regulating theflow of heat transfer fluid trough the cooling heat exchanger 302, andat the same time optionally control the operation of the cooling heatexchanger 302, the temperature of the local heat transfer fluidoutputted from the cooling heat exchanger 302 may be controlled. Theflow valve 305 may be controlled by a second controller 306. The secondcontroller 306 may control the flow valve 305 based on data pertainingto cooling demands of the cooler 301 and/or data pertaining to thetemperature of the local heat transfer fluid in the outlet 26 of thelocal heating system 200 and/or data pertaining to the temperature ofthe local heat transfer fluid in the outlet 304 of the local coolingsystem 300. Data pertaining to cooling demands of the cooler 301 may bedetermined by means of a cooling demand sensor 307 connected to thecooler 301. Data pertaining to the temperature of the heat transferfluid in the outlet 304 of the local heating system 200 may bedetermined by means of the temperature sensor T1 discussed above. Datapertaining to the temperature of the local heat transfer fluid in theoutlet 304 of the local cooling system 300 may be determined by means ofa temperature sensor T2 connected to the outlet 304.

Now turning anew to FIG. 1, the district thermal energy circuit 20 mayfurther comprise a local heating system 250 and/or a local coolingsystem 350.

The district thermal energy circuit 20 may comprise one or more localheating systems 250 and/or one or more local cooling systems 350. Thelocal heating system 250 may be arranged in a building 40. The localcooling system 350 may be arranged in a building 40. The local heatingsystem 250 is connected to the district feed conduit 22 via an inlet 25and connected to the district feed conduit 23 via an outlet 26. Thelocal cooling system 350 is connected to the district return conduit 23via an inlet 25 and connected to the district feed conduit 22 via anoutlet 26.

Now turning to FIG. 4, the local heating system 250 will be discussed.The local heating system 250 can be seen as a thermal energy consumerassembly. The district thermal energy circuit 20 may comprise one ormore thermal energy consumer assemblies.

The local heating system 250 comprises a thermal energy consumer heatexchanger 251, a thermal energy consumer valve 252, a thermal energyconsumer pump 253, a first pressure difference determining device 254and a first controller 255.

The thermal energy consumer heat exchanger 251 is selectively connectedto the district feed conduit 22, being a hot conduit, via the thermalenergy consumer valve 252 and the thermal energy consumer pump 253. Uponselecting the connection of the thermal energy consumer heat exchanger251 to the district feed conduit 22 to be via the thermal energyconsumer valve 252, heat transfer fluid from the district feed conduit22 is allowed to flow into the thermal energy consumer heat exchanger251. Upon selecting the connection of the thermal energy consumer heatexchanger 251 to the district feed conduit 22 to be via the thermalenergy consumer pump 253, heat transfer fluid from the district feedconduit 22 is pumped into the thermal energy consumer heat exchanger251. As will be discussed more in detail below, the choice of allowingheat transfer fluid from the district feed conduit 22 to flow into thethermal energy consumer heat exchanger 251 or pumping heat transferfluid from the district feed conduit 22 into the thermal energy consumerheat exchanger 251, is made based on a local pressure difference betweenthe district feed conduit 22 and the district return conduit 23.

The thermal energy consumer valve 252 and the thermal energy consumerpump 253 may be arranged as separate devices. The thermal energyconsumer valve 252 and the thermal energy consumer pump 253 may bearranged as a single device, in the summary section referred to as aflow regulator. The thermal energy consumer valve 252 and the thermalenergy consumer pump 253 may be arranged in parallel, as illustrated inFIG. 4. The thermal energy consumer valve 252 and the thermal energyconsumer pump 253 may be arranged in series. In this last embodimentwherein the thermal energy consumer valve 252 and the thermal energyconsumer pump 253 is arranged in series the pump is arranged to be setin an inactive state allowing a flow of heat transfer fluid therethrough.

The thermal energy consumer heat exchanger 251 is further connected tothe district return conduit 23, being a cold conduit, for allowingreturn of heat transfer fluid from the thermal energy consumer heatexchanger 251 to the district return conduit 23.

The first pressure difference determining device 254 is adapted todetermine a first local pressure difference, Δp₁, of the districtthermal energy circuit 20. The first local pressure difference ispreferably measured in the vicinity to where the thermal energy consumerheat exchanger 251 is connected to the district thermal energy circuit20. The first pressure difference determining device 254 may comprises afirst hot conduit pressure determining device 254 a and a first coldconduit pressure determining device 254 b. The first hot conduitpressure determining device is arranged to be connected to the districtfeed conduit 22 for measuring a first local pressure of the heattransfer fluid of the district feed conduit 22. The first cold conduitpressure determining device is arranged to be connected to the districtreturn conduit 23 for measuring a first local pressure of the heattransfer fluid of the district return conduit 23. The first localpressure difference device 254 is arranged to determine the first localpressure difference as a pressure difference between the first localpressure of the heat transfer fluid of the district feed conduit 22 andthe first local pressure of the heat transfer fluid of the districtreturn conduit 23. Hence, the first local pressure difference may bedefined as a local pressure difference between a first local pressure ofthe heat transfer fluid of the district feed conduit 22 and a firstlocal pressure of the heat transfer fluid of the district return conduit23. Preferably, the first local pressure of the heat transfer fluid ofthe district feed conduit 22 is measured in the vicinity to where thethermal energy consumer heat exchanger 251 is connected to the districtfeed conduit 22. Preferably, the first local pressure of the heattransfer fluid of the district return conduit 23 is measured in thevicinity to where the thermal energy consumer heat exchanger 251 isconnected to the district return conduit 23.

The first pressure difference determining device 254 may be implementedas a hardware device, a software device, or as a combination thereof.The first pressure difference determining device 254 is arranged tocommunicate the first local pressure difference, Δp₁, to the firstcontroller 255.

The first controller 255 may be implemented as a hardware controller, asoftware controller, or as a combination thereof. The first controller255 is arranged to selectively control the use of either the thermalenergy consumer valve 252 or the thermal energy consumer pump 253. Thefirst controller 255 is arranged to perform the selective control basedon the first local pressure difference provided by the first pressuredifference determining device 254. The first controller 255 is arrangedto communicate with the thermal energy consumer valve 252 and thethermal energy consumer pump 253 for controlling the thermal energyconsumer valve 252 and the thermal energy consumer pump 253. The firstcontroller 255 is arranged to selectively control the use of the thermalenergy consumer valve 252 when the first local pressure differenceindicates that the first local pressure of the heat transfer fluid ofthe district feed conduit 22 is larger than the first local pressure ofthe heat transfer fluid of the district return conduit 23. The firstcontroller 255 is arranged to selectively control the use of the thermalenergy consumer pump 253 when the first local pressure differenceindicates that the first local pressure of the heat transfer fluid ofthe district feed conduit 22 is lower than or equal to the first localpressure of the heat transfer fluid of the district return conduit 23.

The thermal energy consumer heat exchanger 251 is arranged to transferthermal energy from heat transfer fluid to surroundings of the thermalenergy consumer heat exchanger 251. The heat transfer fluid returned tothe district return conduit 23 has a temperature lower than the firsttemperature. Preferably, thermal energy consumer heat exchanger 251 iscontrolled such that the temperature of the heat transfer fluid returnedto the district return conduit 23 is equal to the second temperature.

Again turning to FIG. 4, the local cooling system 350 will be discussed.The local cooling system 350 can be seen as a thermal energy generatorassembly. The district thermal energy circuit 20 may comprise one ormore thermal energy generator assemblies.

The local cooling system 350 comprises a thermal energy generator heatexchanger 351, a thermal energy generator valve 252, a thermal energygenerator pump 353, a second pressure difference determining device 354,and a second controller 355.

The thermal energy generator heat exchanger 351 is selectively connectedto the district return conduit 23 via the thermal energy generator valve352 and the thermal energy generator pump 353. Upon selecting theconnection of the thermal energy generator heat exchanger 351 to thedistrict return conduit 23 to be via the thermal energy generator valve352, heat transfer fluid from the district return conduit 23 is allowedto flow into the thermal energy generator heat exchanger 351. Uponselecting the connection of the thermal energy generator heat exchanger351 to the district return conduit 23 to be via the thermal energygenerator pump 353, heat transfer fluid from the district return conduit23 is pumped into the thermal energy generator heat exchanger 351. Aswill be discussed more in detail below, the choice of allowing heattransfer fluid from the district return conduit 23 to flow into thethermal energy generator heat exchanger 351 or pumping heat transferfluid from the district return conduit 23 into the thermal energygenerator heat exchanger 351, is made based on a local pressuredifference between the district feed conduit 22 and district returnconduit 23.

The thermal energy generator valve 352 and the thermal energy generatorpump 353 may be arranged as separate devices. The thermal energygenerator valve 352 and the thermal energy generator pump 353 may bearranged as a single device, in the summary section referred to as aflow regulator. The thermal energy generator valve 352 and the thermalenergy generator pump 353 may be arranged in parallel, as illustrated inFIG. 4. The thermal energy generator valve 352 and the thermal energygenerator pump 353 may be arranged in series. In this last embodimentwherein the thermal energy generator valve 352 and the thermal energygenerator pump 353 is arranged in series the pump is arranged to be setin an inactive state allowing a flow of heat transfer fluid therethrough.

The thermal energy generator heat exchanger 351 is further connected tothe district feed conduit 22 for allowing return of heat transfer fluidfrom the thermal energy generator heat exchanger 351 to the districtfeed conduit 22.

The second pressure difference determining device 354 is adapted todetermine a second local pressure difference, Ape, of the districtthermal energy circuit 20. The second local pressure difference ispreferably measured in the vicinity to where the thermal energygenerator heat exchanger 351 is connected to the district thermal energycircuit 20. The second pressure difference determining device 354 maycomprises a second hot conduit pressure determining device 354 a and asecond cold conduit pressure determining device 354 b. The second hotconduit pressure determining device is arranged to be connected to thedistrict feed conduit 22 for measuring a second local pressure of theheat transfer fluid of the district feed conduit 22. The second coldconduit pressure determining device 354 b is arranged to be connected tothe district return conduit 23 for measuring a second local pressure ofthe heat transfer fluid of the district return conduit 23. The secondlocal pressure difference device 354 is arranged to determine the secondlocal pressure difference as a pressure difference between the secondlocal pressure of the heat transfer fluid of the district feed conduit22 and the second local pressure of the heat transfer fluid of thedistrict return conduit 23. Hence, the second local pressure differencemay be defined as a local pressure difference between a second localpressure of the heat transfer fluid of the district feed conduit 22 anda second local pressure of the heat transfer fluid of the districtreturn conduit 23. Preferably, the second local pressure of the heattransfer fluid of the district feed conduit 22 is measured in thevicinity to where the thermal energy generator heat exchanger 351 isconnected to the district feed conduit 22. Preferably, the second localpressure of the heat transfer fluid of the district return conduit 23 ismeasured in the vicinity to where the thermal energy generator heatexchanger 351 is connected to the district return conduit 23.

The second pressure difference determining device 354 may be implementedas a hardware device, a software device, or as a combination thereof.The second pressure difference determining device 354 is arranged tocommunicate the second local pressure difference, Δp₂, to the secondcontroller 355.

The second controller 355 may be implemented as a hardware controller, asoftware controller, or as a combination thereof. The second controller355 is arranged to selectively control the use of either the thermalenergy generator valve 352 or the thermal energy generator pump 353. Thesecond controller 355 is arranged to perform the selective control basedon the second local pressure difference provided by the second pressuredifference determining device 354. The second controller 355 is arrangedto communicate with the thermal energy generator valve 352 and thethermal energy generator pump 353 for controlling the thermal energygenerator valve 352 and the thermal energy generator pump 353. Thesecond controller 355 is arranged to selectively control the use of thethermal energy generator valve 352 when the second local pressuredifference indicates that the second local pressure of the heat transferfluid of the district return conduit 23 is larger than the second localpressure of the heat transfer fluid of the district feed conduit 22. Thesecond controller 355 is arranged to selectively control the use of thethermal energy generator pump 353 when the second local pressuredifference indicates that the second local pressure of the heat transferfluid of the district return conduit 23 is lower than or equal to thesecond local pressure of the heat transfer fluid of the district feedconduit 22.

The thermal energy generator heat exchanger 351 is arranged to transferthermal energy from its surroundings to heat transfer fluid. The heattransfer fluid returned to district feed conduit 22 has a temperaturehigher than the second temperature. Preferably, thermal energy generatorheat exchanger 351 controlled such that the temperature of the heattransfer fluid returned to the district feed conduit 22 is equal to thefirst temperature.

In the in FIG. 4 shown embodiment the first and second pressuredifference determining devices 254; 354 are two physically differentpressure difference determining devices. However, according to anotherembodiment one specific local thermal energy consumer assembly 250 andone specific local thermal energy generator assembly 350 may share thesame pressure difference determining device. Hence, the first and secondpressure difference determining devices 254; 354 may physically be thesame pressure difference determining device. According to a furtherembodiment two specific local thermal energy consumer assemblies 250 mayshare the same pressure difference determining device. According to ayet another embodiment two specific local thermal energy generatorassemblies 350 may share the same pressure difference determiningdevice.

In the in FIG. 4 shown embodiment the first and second controllers 255;355 are two physically different controllers. However, according toanother embodiment one specific local thermal energy consumer assembly250 and one specific local thermal energy generator assembly 350 mayshare the same controller. Hence, the first and second controller 255;355 may physically be the same controller. According to a furtherembodiment two specific local thermal energy consumer assemblies 250 mayshare the same controller. According to a yet another embodiment twospecific local thermal energy generator assemblies 350 may share thesame controller.

Preferably, the demand to inhale or exhale heat using the thermal energyconsumer heat exchangers 251 and the thermal energy generator heatexchangers 351 is made at a defined temperature difference. Atemperature difference of 8-10° C. corresponds to optimal flows throughthe thermal energy consumer heat exchangers 251 and the thermal energygenerator heat exchangers 351.

The local pressure difference between the district feed conduit 22 andthe district return conduit 23 may vary along the district thermalenergy circuit 20. Especially, the local pressure difference between thedistrict feed conduit 22 and the district return conduit 23 may varyfrom positive to negative pressure difference seen from one of thedistrict feed or return conduits, 22, 23. Hence, sometimes a specificlocal thermal energy consumer/generator assembly 250, 350 may need topump heat transfer fluid through the corresponding thermal energyconsumer/generator heat exchanger 251, 351 and sometimes the specificlocal thermal energy consumer/generator assembly 250, 350 may need tolet heat transfer fluid flow through the corresponding thermal energyconsumer/generator heat exchanger 251, 351. Accordingly, it will bepossible to let all the pumping within the system to take place in thelocal thermal energy consumer/generator assemblies 250, 350. Due to thelimited flows and pressures needed small frequency controlledcirculation pumps may be used.

The thermal energy consumer pump 253 and/or the thermal energy generatorpump 353 may for example be a frequency controlled circulation pump.

The thermal energy consumer valve 252 and/or the thermal energygenerator valve 352 may be a regulation valve.

With reference to FIG. 5 a method of providing mechanical work andheating heat transfer fluid of a district thermal energy circuit 20 isdisclosed. The method comprises one or more of the following acts. Theacts may be performed in any order suitable.

Supplying S500 a flow of geothermally heated water from a geothermalheat source 10 to a boiler 51 which is connected to the geothermal heatsource 10.

Exchanging S502 heat from the incoming flow of geothermally heated waterto superheat a working medium. The heat is exchanged from the incomingflow of geothermally heated water by a heat exchanger 52 a,52 b, 52 c ofthe boiler 51.

Expanding S504 the superheated working medium in an expander to therebyprovide mechanical work. The mechanical work may be transferred to agenerator to transform the mechanical work to electrical power. Theelectrical power may by way of example be supplied to the electricalgrid.

Transforming, S506, at a condenser 55, the expanded working medium toliquid phase by heating a heat transfer fluid of a district feed conduit22 in the district thermal energy circuit 20 to a temperature of 5-30°C.

The flow of local heat transfer fluid is circulated in the districtthermal energy distributing system 20 via the district feed conduit 22to local heating or cooling systems 200, 250, 300, 350 arranged inbuildings 40 and then back to the condenser 55 via the district returnconduit 23. The act of circulating is preferably performed using aplurality the local circulation pumps 28 or by a central circulationpump 27.

Heat may be extracted from the local heat transfer fluid flowing in thelocal feed conduit 22 at the local heating system 200, 250 in each ofthe plurality of buildings 40. The extracted heat may be used forproviding hot tap water and/or comfort heating to the respectivebuilding 40. Also, heat may be extracted from one of the plurality ofbuildings 40 at a cooling system 300, 350.

The person skilled in the art realizes that the present invention by nomeans is limited to the preferred embodiments described above. On thecontrary, many modifications and variations are possible within thescope of the appended claims.

For example, in the in FIG. 3 shown embodiment the flow valve 305 isarranged in the outlet 304 of the cooling heat exchanger 302. However,the flow valve 305 may alternatively be arranged in the inlet 303 of thecooling heat exchanger 302.

In the in FIG. 3 shown embodiment, the first and second controllers 204,306 are illustrated as separate controllers. However, alternatively thefirst and second controllers 204, 306 may be combined into a singlecontroller.

In the in FIG. 1 shown embodiment the central circulation pump 27 isillustrated to be located at the inlet to the condenser 55. However, itis realized that the central circulation pump 27 may be arranged at anyposition within the district thermal energy circuit 20.

In the in FIG. 3 shown embodiment, the local heat transfer fluid exitingthe local cooling system 300 via the outlet 304 of the cooling heatexchanger 302 is feed to the district return conduit 23. However,alternatively or in combination, the heat transfer fluid exiting thelocal cooling system 300 via the outlet 304 may be feed to the districtfeed conduit 22. Feeding of the heat transfer fluid exiting the localcooling system 300 via the outlet 304 may be controlled by the secondcontroller 306. The control of the feeding of the heat transfer fluidexiting the local cooling system 300 via the outlet 304 to the districtfeed and/or return conduits 22, 23 may be based on the temperaturemonitored by the second sensor T2.

Further, the heating and cooling systems have been exemplified with one,respectively two temperature sensors T1 and T1-T2, respectively. It isto be understood that the number of temperature sensors and theirpositions may change. It is also to be understood that additionalsensors may be introduced to the system depending on desired input tothe first and second controllers 204, 306 and desired complexity.Especially, the first and second controllers 204, 306 may be arranged tocommunicate with the heat emitters 202 and/or coolers 301 locallyarranged in the buildings 40 to take local settings into account.

Additionally, variations to the disclosed embodiments can be understoodand effected by the skilled person in practicing the claimed invention,from a study of the drawings, the disclosure, and the appended claims.

1. A district energy distributing system comprising: a geothermal powerplant comprising: a first circuit comprising: a feed conduit for anincoming flow of geothermally heated water from a geothermal heatsource; a boiler comprising a heat exchanger configured to exchange heatfrom the incoming flow of geothermally heated water to superheat aworking medium of a second circuit of the geothermal power plant; areturn conduit for a return flow of cooled water from the boiler to thegeothermal heat source; wherein the second circuit comprises: the boilerconfigured to superheat the working medium of the second circuit; anexpander connected to the boiler and configured to allow the superheatedworking medium to expand and to transform the expansion to mechanicalwork; and a condenser configured to transform the expanded workingmedium to liquid phase and to heat a heat transfer fluid of a districtthermal energy circuit; wherein the district thermal energy circuitcomprises: a district feed conduit, and a district return conduit,wherein the district feed conduit is configured to allow heat transferfluid of a first temperature to flow there through, and wherein thedistrict return conduit is configured to allow heat transfer fluid of asecond temperature to flow there through, wherein the second temperatureis lower than the first temperature; a plurality of local heatingsystems, each having an inlet connected to the district feed conduit andan outlet (26) connected to the district return conduit, wherein eachlocal heating system is configured to provide hot water and/or comfortheating to a building, and wherein each of the local heating systemscomprises: a thermal energy consumer heat exchanger selectivelyconnected to the district feed conduit via a thermal energy consumervalve for allowing heat transfer fluid from the district feed conduit toflow into the thermal energy consumer heat exchanger, selectivelyconnected to the district feed conduit via a thermal energy consumerpump for pumping heat transfer fluid from the district feed conduit intothe thermal energy consumer heat exchanger, and connected to thedistrict return conduit for allowing return of heat transfer fluid fromthe thermal energy consumer heat exchanger to the district returnconduit, wherein the thermal energy consumer heat exchanger is arrangedto transfer thermal energy from heat transfer fluid to surroundings ofthe thermal energy consumer heat exchanger, such that heat transferfluid returned to the district return conduit has a temperature lowerthan the first temperature and preferably a temperature equal to thesecond temperature: a pressure difference determining device configuredto determine a local pressure difference, Δp1, between the district feedconduit and the district return conduit; and a controller configured to,based on the local pressure difference, selectively control the use ofeither the thermal energy consumer valve or the thermal energy consumerpump; wherein the condenser is configured to heat transfer fluid of thedistrict feed conduit to a temperature of 5-30° C.
 2. The districtenergy distributing system according to claim 1, wherein the geothermalheat source is a deep geothermal heat source.
 3. The district energydistributing system according to claim 1, wherein the expander is a gasturbine.
 4. The district energy distributing system according to claim1, wherein the expander is configured to allow the superheated workingmedium to expand to receive an outgoing temperature of 10-40° C.
 5. Thedistrict energy distributing system according to claim 1, wherein theboiler is configured to superheat the liquefied working medium from thecondenser.
 6. The district energy distributing system according to claim1, wherein the geothermal power plant further comprises a generatorconfigured to transform the mechanical work into electrical power. 7.The district energy distributing system according to claim 1, whereinthe geothermal heat source is configured to geothermally heat the cooledwater returned via the return conduit to a temperature of 100-250° C. 8.The district energy distributing system according to claim 1, whereinthe first circuit further comprises a suction pump configured to drawgeothermally heated water from the geothermal heat source to the teedconduit, and pressurize the geothermally heated water such that it is inliquid phase in the feed conduit.
 9. The district energy distributingsystem according to claim 1, wherein the boiler is configured toexchange heat from the incoming flow of geothermally heated water suchthat the cooled water in the return conduit has a temperature of 10-40°C.
 10. The district energy distributing system according to claim 1,wherein the district feed conduit together with the district returnconduit have a heat transfer coefficient greater than 2.5 W/(mK) whenparallel arranged in ground.
 11. (canceled)
 12. The district energydistributing system according to claim 11, wherein the controller isconfigured to selectively use the thermal energy consumer valve when thelocal pressure difference indicates that a local pressure of the heattransfer fluid of the district feed conduit is larger than a localpressure of the heat transfer fluid of the district return conduit,wherein the controller is configured to selectively use the thermalenergy consumer pump when the first local pressure difference indicatesthat the first local pressure of the heat transfer fluid of the districtfeed conduit is lower than or equal to the first local pressure of theheat transfer fluid of the district return conduit.
 13. The districtenergy distributing system according to claim 1, wherein each of theplurality of local heating systems is configured to extract heat fromheat transfer fluid entering the local heating system via the inlet andreturn the thereafter cooled heat transfer fluid to the district returnconduit via the outlet, wherein each of the plurality of local heatingsystems is configured to return local heat transfer fluid having atemperature in the range of −5-15° C.
 14. The district energydistributing system according to claim 1, wherein the district feedconduit and district return conduit are dimensioned for pressures up to0.6 MPa, 1 MPa, or 1.6 MPa.
 15. (canceled)